Cell Division

Cell Cycle, Mitosis, and Cytokinesis

Chromosomes Are bundled packages

that contain genetic information (DNA).

Must be copied before cell division begins.

Make the process of separating DNA during cell division possible.

Chromosomes

There are two types– Prokaryotic

• Is a single, circular chromosome that contains almost all the cell’s genetic information.

Chromosomes

• Eukaryotic• Formation process

– DNA and histones combine to form chromatin.

– Chromatin coils tightly to form beadlike structures (nucleosomes).

– Nucleosomes are packed together to form thick fibers.

– Thick fibers form super coils which become chromosomes.

Chromosomes

The Cell Cycle

• Is a series of events that cells go through as they grow and divide.

The Cell Cycle

• Prokaryotic cell cycle– Is known as binary

fission• Includes a regular,

and rapid, pattern of growth, DNA, replication, and cell division.

• Produces two genetically identical cells.

The Cell Cycle

• Eukaryotic cell cycle– Consists of interphase and cell division.

– Interphase is divided into three phases: Gap1 (G1),

Synthesis (S), and Gap2 (G2).

• Cell growth occurs during G1 phase.

– New proteins and organelles are synthesized

• DNA replication occurs during the synthesis (S) phase.

– New DNA is synthesized when chromosomes are replicated.

– Cells have double the amount of DNA at the end of this phase.

The Cell Cycle

• Eukaryotic cell cycle– The cell is prepared for cell division during G2.

• This is the shortest phase of interphase.• Organelles and molecules required for cell

division are produced.– Cell division (M phase) includes mitosis and

cytokinesis.• Occurs rapidly• In mitosis the cell nucleus is divided.• In cytokinesis the cytoplasm is divided.

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Mitosis

• Is divided into four phases: prophase, metaphase, anaphase, and telophase.

Mitosis

• Prophase– Is the longest phase of mitosis.– Events

• The genetic material inside the nucleus condenses.

• Duplicated chromosomes become visible– Duplicated DNA strands are attached to a

centromere.– Each DNA strand of the duplicated chromosome is a

chromatid.

Mitosis

• Metaphase– Is the shortest phase of mitosis– Events

• The centromeres of the duplicated chromosomes line up across the center of the cell.

• The spindle fibers connect the centromeres of each chromosome to the two poles of the spindle.

Mitosis

Mitosis

• Anaphase– Events

• The chromosomes separate from each other.• Chromosomes move to opposite ends of the

cell.• Spindle fibers begin to break down.

Mitosis

Mitosis

• Telophase– Events

• Each cell has a complete set of chromosomes– Chromosomes become a tangle of chromatin.

• A nuclear envelope forms around each new set of chromosomes.

• The spindle fibers disappear.

Mitosis

Mitosis

• Cytokinesis– Usually occurs at the same time as

telophase.– Cells divide into new cells; each has its

own nucleus.– Plant cells form a new cell wall in the

center of the cell.

Animal vs. Plant Cytokinesis